Chicago's bet on green roofs

Hari Sreenivasan, for the PBS Newshour:

One of Chicago’s most beautiful gardens is one very few people get to see, a 23,000-square-foot green roof that sits on top of City Hall. The difference a green roof makes is measurable. That side of City Hall’s roof used to be traditional black, like most roofs. On a hot day, when it was 90 degrees out, they came out and measured the surface temperature. It was 169 degrees, vs. this side of City Hall, where they have a green roof, and the surface temperature was 90 degrees, almost an 80-degree difference.

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